1. Field of the Invention
This invention generally relates to the measurement of a multiple phase flow. Here, microwave radiation is used to measure the two-phase fluid content of oil field flowlines and also the two-phase fluid content of fluid-saturated porous media.
2. Background Information
A multiple fluid mixture has at least one physically distinct and mechanically separable fluid within at least one other physically distinct and mechanically separable fluid in a physical/chemical system. In the case at hand a multiple fluid mixture would be something such as a combination of water and oil.
Some of the factors that complicate the measurement of the multiple fluid mixture are: whether the mixture is in a static or dynamic state; and whether the method is intrusive or non-intrusive. One simple method of analyzing a multiple fluid mixture involves capturing of a sample volume of the mixture and then analyzing it (or simply allowing the mixture to separate into its component phases). This method, however, is an intrusive one and involves too much time and effort to capture a sample volume. Furthermore, when captured, there is no guarantee that the sample volume is an adequate representation of the entire sample. If so, the calculation for the total concentration of the two components in the mixture will be erroneous. For that reason a non-intrusive method would be preferable.
Multiple fluid mixtures may also be measured by subjecting a sample (either in a static or dynamic state) to photonic laser, or infra-red radiation. In these cases, a multiple fluid mixture is subjected to the specific radiation and the attenuation of the radiation is used to calculate the component phases. See U.S. Pat. Nos. 4,157,470 to Kotuka et al.; 4,470,647 to Chraphyvy et al.; and 4,394,575 to Nelson; see also V. E. Shrock, "Radiation Attenuation Techniques in Two-Phase Flow Measurements", Nat'l ASME/AICHE, Heat Transfer Conference, Minneapolis (1969); and Davis, "VHF Electrical Measurement of Saturations in Laboratory Corefloods", SPE 8847 (1980).
The other factor that was mentioned above, i.e., whether the mixture is in a static or a dynamic state, would reflect mainly on the particulars of the measurement system. For example, in most applications it is most desirable to measure the mixture when it is in a fluid or flowing state. A common example would be an oil field flowline pipe that may transport liquid. However, there are examples where it may be desirable to measure multiple fluids in a static system. For example, a laboratory situation may be set up in which a sample petroleum formation, containing a porous medium (such as Berea Sandstone), has a two-phase mixture. Both cases could be applications of the same measurement technique.
The techniques described above are useful in understanding how fluid concentrations may be measured in a multiple fluid mixture. However, as applied to petroleum applications, i.e., multiple fluid mixtures of water and oil in a flowline or a test core, microwaves work to distinguish between multiple fluids. Some work has already been done in which microwaves are used to determine the concentration of multiple fluids, as outlined below. The devices disclosed in U.S. Pat. Nos. 4,167,736 to Tomlinson; 4,196,385 to Vesterpaard et al.; 4,423,623 to Ho et al.; and 4,503,384 to Nagy et al. all are intrusive into the fluid that they are measuring and are undesirable because of that fact. U.S. Pat. Nos. 4,289,020 and 4,301,400, to Paap, show devices that manipulate the fluid channel through which crude oil flows and are undesirable because they contain "dead spaces" where the flow may eddy and throw off the measurement system. U.S. Pat. No. 3,586,971 to Besido shows a device that monitors the moisture content in the sheets of material. It uses a method that detects a resonant frequency shift only. U.S. Pat. No. 3,818,333, to Walker, shows a microwave window and antenna, but does not disclose how measurements are made to determine fluid content. The following patents are issued to Lorne A. Davis et al. U.S. Pat. No. 4,519,982 discloses a device that scans a two-dimensional sample. U.S. Pat. Nos. 4,482,634 and 4,490,676 disclose a method ('634) and an apparatus ('676) for monitoring fluid in a core of material. However, both patents only measure power level, not phase shift. U.S. Pat. Nos. 4,486,714 and 4,543,821 use microwave circuitry that is similar to U.S. Pat. No. 4,482,634, but show different methods of fluid delivery to a test core. Two articles relate to some of these patents and are: Haskin and Davis, "A Comparison of Laboratory Linear and Pattern Flow Chemical Floods Using a Volumetric Linear Scaling Concept for Oil Saturation and Distributions", SPE 10197 (1981) (see U.S. Pat. No. 4,519,982); Brost and Davis, "Determination of Oil Saturation and Distributions in Field Cores by a Microwave Spectroscopy", SPE 10110 (1981) (see U.S. Pat. Nos. 4,482,634 and 4,490,676).
Other articles disclose the use of microwaves to measure fluid contents. R. W. Parsons was one of the first investigators to disclose a method to determine in situ saturations of multiple fluid phases in a laboratory coreflood using microwave attenuation, see Parsons, "Microwave Attenuation--A New Tool for Monitoring Situations in Laboratory Flooding Experiments", Soc. Pet. Eng. Jour. 302 (Aug., 1975). However, the signal penetration depth in this method is limited to one inch and the frequency is 21.26 Gigahertz. P. E. Baker discusses a similar method (at the end of the Parsons' paper, see page 309). Bentsen and Saeedi show a method that is similar to Parsons, see Bentsen and Saeedi, "Liquid-Immiscible Displacement in Unconsolidated Porous Media", Jour. Can. Pet. Tech. 93 (Jan.-Mar. 1981). Their method measures only microwave attenuation, has a penetration depth of only 1.27 centimeters, and operates on a microwave frequency of 27 Gigahertz. Wasan et al. also show a method similar to Parsons, see Wasan et al., "Microwave Spectroscopy Analysis of Surfactant/Polymer Flooding: Interrelationships Between Chemical Slug Properties, Coalescence Phenomena, and Tertiary Oil Recovery", SPE 8327 (1979). For example, Wasan et al. measure microwave attenuation using a frequency of 21.83 Gigahertz. Another similar device is described in Gladfelter and Gupta, "The Effect of Fractional Flow Hysteresis on Recovery of Tertiary Oil", Soc. Pet. Eng. Jour. 509 (Dec., 1980). Here, measurements of multiple fluids are made with microwave attenuation and depth penetration is limited to 1.91 centimeters. An article that reviews all the current methods to measure multiple fluids and petroleum applications is Saraf, "Methods of In-situ Saturation Determination During Core Tests Involving Multiphase Fluid Flow", Report 1981-6 Petroleum Recovery Institute (Mar., 1981).
These references mostly use only one measurement technique, i.e., signal attenuation, to determine fluid concentrations. This has some drawbacks, in that: some physical properties are masked in different flow regimes when you use signal attenuation; you may be limited to determining the concentrations of only two fluid phases (with one measurement technique); and you do not have a confirmation of the fluid concentrations when you use a single method.